Several types of genetic abnormalities are known to affect the development of the early mouse embryo. One group consists of a variety of recessive alleles at the several different loci, including those for agouti coat color (a) and oligosyndactyly (Os). In addition to these presumed single locus mutations (some locus mutations (some of which are actually deletions which could include more than one locus), all of the known autosomal monosomies also result in peri-implantation lethality in the mouse, as they do in man. Beyond these effects of alterations in gene structure or number, disomy for single chromosomes may, by virtue of the effects of imprinting, have dire effects on embryonic viability and/or development. In approaching the mechanisms by which these genetic abnormalities affect early development, two new and quite powerful methodologies will be used. One is the polymerase chain reaction (PCR) which, when appropriate DNA markers are employed, makes possible the genotyping of individual embryos. The second is the computer-based analysis of two-dimensional polyacrylamide gel electrophoretograms (PAGE), which makes possible the qualitative and quantitative comparison of matched sets of embryos or cells. Using these approaches, the peri-implantation effects of the recessive lethal mutations, ax, al, a16H, and Ay, at the agouti locus and of the Os mutation, the effects of chromosomal monosomy, and consequences of gametic imprinting will be investigated. To accomplish this, the time and nature of the lethality of homozygous lethal mutations at the agouti locus will be studied morphologically by light and electron microscopy. Defective or missing gene products in embryos homozygous for mutations at the agouti and Os loci will be detected by PAGE of radioactively labelled embryonic proteins coupled with the computer-based analysis of matched sets of gels using the QUEST system. Similar PAGE studies will be undertaken with monosomic embryos to detect gene-dosage related reductions in the synthesis of specific proteins and also to identify secondary effects resulting from alterations in the dosage of regulatory molecules. The development of monosomic embryos lacking either a paternal or maternal chromosome will be compared to determine whether gametic imprinting affects the pathogenesis of the lethality of monosomy, and the PAGE system will be used to determine whether effects of gametic imprinting on the synthesis of proteins by pre- and peri-implantation embryos are detectable. Finally, the synthesis of proteins by disomic embryonic stem cells and fibroblasts of the two parental types will be analyzed to detect differences resulting from the imprinting process in the expression of specific genes. In many instances, microsequencing of proteins that are qualitatively or quantitatively altered or are missing will be undertaken to permit identification of the responsible genes. These studies will provide insight into gene expression and the genetic regulation of embryonic development during the peri- implantation period.